Temporary Capture of Asteroid Ejecta into Periodic Orbits: Application to JAXA’s Hayabusa2 Impact Event

Abstract

In this paper, we study the dynamical environment around asteroids to investigate whether ejecta particles from an impact event (artificial or natural) could be temporarily trapped in periodic orbits. If such particles remain about an asteroid, they could potentially jeopardize an orbiting spacecraft in the event of a collision. We make use of invariant manifold theory to assess the conditions - impact location, particle radius, ejection velocity - that cause ejecta particles to get captured in periodic orbits. The analysis is carried out within the dynamical framework of the perturbed Augmented Hill Problem, which takes into account the solar radiation pressure, the effect of eclipses, and the J20 and J40 terms of the asteroid's gravity potential in its spherical harmonics expansion. We analyze millimeter- to centimeter-sized particles and captures into three families of periodic orbits that are robust to large values of the solar radiation pressure acceleration – the traditional a and g’ families of the Hill Problem and the southern halo orbits. We go on to find the impact locations from where ejecta particles are most likely to be captured into periodic orbits via their stable manifolds. As such, we recover the sets of initial states that lead ejecta to temporary orbital capture and show that solar radiation pressure and, subsequently, eclipses, cannot be neglected in these analyses. We apply our analyses to the specific case of JAXA's Hayabusa2 mission that successfully carried out its Small Carry-on Impactor (SCI) operation at asteroid Ryugu in April 2019. For this event, we identify locations on the Sun side of the asteroid at medium latitudes as the best impact locations.